Massimo GiovannozziOxford - July 4th Manipulation of transverse beam distribution in circular accelerators: beam splitting by particles trapping into resonance islands M. Giovannozzi Summary: Introduction Introduction Present multi-turn extraction Present multi-turn extraction New multi-turn extraction (MTE) New multi-turn extraction (MTE) Other applications Other applications Measurement results Measurement results Conclusions Conclusions

Massimo GiovannozziOxford - July 4th Introduction - I Three approaches are normally used to extract beam from a circular machine: Fast Extraction (one turn) A kicker (fast dipole) displaces the beam from nominal closed orbit. A kicker (fast dipole) displaces the beam from nominal closed orbit. A septum magnet deflects displaced beam towards transfer line. A septum magnet deflects displaced beam towards transfer line. This extraction can be used both to transfer beam towards a ring or an experimental area. This extraction can be used both to transfer beam towards a ring or an experimental area. Slow Extraction (millions turns) The separatix of the third- order resonance increases particles amplitude until they jump beyond the septum. The separatix of the third- order resonance increases particles amplitude until they jump beyond the septum. The tune is changed to shrink the stable region, thus pushing the particles towards larger amplitudes. The tune is changed to shrink the stable region, thus pushing the particles towards larger amplitudes. This extraction is used to transfer beam towards an experimental area. This extraction is used to transfer beam towards an experimental area. What is in between? Multi-turn!

Massimo GiovannozziOxford - July 4th Introduction - II Multi-turn extraction The beam has to be manipulated to increase the effective length beyond the machine circumference. This extraction mode is used to transfer beam between circular machines. AT CERN this mode is used to transfer the proton beam between PS and SPS. In the SPS the beam is used for Fixed Target physics (broad sense) Neutrino experiments (until 1998) CERN Neutrino to Gran Sasso (CNGS) (from 2006) These beams are high-intensity (about 3×10 13 p in the PS).

Massimo GiovannozziOxford - July 4th Present multi-turn extraction – I First PS batch Second PS batch Gap for kicker C SPS = 11 C PS PSPS SPS circumference Beam current transformer in the PS/SPS transfer line (total spill duration ms) (total spill duration ms)

Massimo GiovannozziOxford - July 4th Electrostatic septum blade Present multi-turn extraction – II Length Kicker strength Four turns Fifth turn X X Slow bump Electrostatic septum (beam shaving) Extraction septum Kicker magnets used to generate a closed orbit bump around electrostatic septum Extraction line E field =0 E field 0

Massimo GiovannozziOxford - July 4th Present multi-turn extraction –III The main drawbacks of the present scheme are: Losses (about 15% of total intensity) are unavoidable due to the presence of the electrostatic septum used to slice the beam. The electrostatic septum is irradiated. This poses problems for hands-on maintenance. The phase space matching is not optimal (the various slices have fancy shapes), thus inducing betatronic mismatch in the receiving machine, i.e. emittance blow-up. The slices have different emittances and optical parameters.

Massimo GiovannozziOxford - July 4th Novel multi-turn extraction – I The main ingredients of the novel extraction: The beam splitting is not performed using a mechanical device, thus avoiding losses. Indeed, the beam is separated in the transverse phase space using The beam splitting is not performed using a mechanical device, thus avoiding losses. Indeed, the beam is separated in the transverse phase space using Nonlinear magnetic elements (sextupoles ad octupoles) to create stable islands. Slow (adiabatic) tune-variation to cross an appropriate resonance. This approach has the following beneficial effects: This approach has the following beneficial effects: Losses are reduced (virtually to zero). The phase space matching is improved with respect to the present situation. The beamlets have the same emittance and optical parameters.

Massimo GiovannozziOxford - July 4th Model used in numerical simulations Standard approach: nonlinear elements represented as a single kick at the same location in the ring (Hénon-like polynomial maps). Vertical motion neglected. Normalised (adimensional co-ordinates). QuadrupolesSextupoleOctupole The linear tune is time-dependent

Massimo GiovannozziOxford - July 4th Novel multi-turn extraction – II Right: intermediate phase space topology. Islands are created near the centre. Bottom: final phase space topology. Islands are separated to allow extraction. Left: initial phase space topology. No islands.

Massimo GiovannozziOxford - July 4th Novel multi-turn extraction - III Tune variation Phase space portrait Simulation parameters: Hénon-like map (i.e. 2D polynomial – degree 3 - mapping) representing a FODO cell with sextupole and octupole

Massimo GiovannozziOxford - July 4th Novel multi-turn extraction – IV Final stage after turns (about 42 ms for CERN PS) About 6 cm in physical space Slow (few thousand turns) bump first (closed distortion of the periodic orbit) Fast (less than one turn) bump afterwards (closed distortion of periodic orbit) B field 0 B field = 0 At the septum location

Massimo GiovannozziOxford - July 4th Novel multi-turn extraction - V The original goal of this study was to find a replacement to the present Continuous Transfer used at CERN for the high-intensity proton beams. However the novel technique proved to be useful also in different context, e.g. The same approach can be applied for multi-turn injection (time-reversal property of the physics involved). multi-turn extraction over a different number of turns can be designed, provided the appropriate resonance is used. Multiple multi-turn extractions could be considered, e.g. to extract the beam remaining in the central part of phase space.

Massimo GiovannozziOxford - July 4th Novel multi-turn extraction with other resonances - I Tune variation Phase space portrait Simulation parameters: Hénon-like map with sextupole and octupole The third- order resonance is used, thus giving a three-turn extraction

Massimo GiovannozziOxford - July 4th Novel multi-turn extraction with other resonances - II The fifth-order resonance is used, thus giving a six-turn extraction The second-order resonance is used, thus giving a two-turn extraction

Massimo GiovannozziOxford - July 4th Non-linear elements can be used to make the fourth-order resonance unstable by canceling the amplitude detuning. Possible applications: Four-turn extraction. Deplete the core region to achieve a better intensity sharing. Novel multi-turn extraction: 4 th order unstable resonance - new application! Master thesis Diego Quatraro

Massimo GiovannozziOxford - July 4th Novel multi-turn injection: new application! Simulation parameters: Third-order polynomial map representing a FODO cell with sextupole and octupole The fourth-order resonance is used for a four-turn injection Tune variation Phase space portrait Efficient method to generate hollow beams!

Massimo GiovannozziOxford - July 4th Novel multi-turn injection: new application! Possible applications: transverse shaping of beam distribution. Observation: the proposed method seems to be more efficient in generating smaller emittance beams than standard multi-turn injection! M. Giovannozzi, J. Morel, PRST-AB, 10, (2007) Standard hollow beam distribution Flat beam distribution obtained by injecting a fifth turn in the centre.

The capture process - I Quantitative analysis needed: To control sharing between core and beamlets. To control the emittance sharing. Adiabatic theory is the key concept: Probability trapping is proportional to the speed of variation of the islands surface. It is possible to account for the loss of adiabaticity close to the separatrix. 2D case seems under control. The 4D case requires the usual conditions: weak coupling between the two degrees of freedom no low order resonances in the vertical plane Massimo GiovannozziOxford - July 4th

Massimo GiovannozziOxford - July 4th The capture process - II Initial gaussian distribution Particles in island 2 Particles in island 4 Particles in island 6 Particles in island 8 Particles in beam core

The capture process - III Under these conditions: Scaling law for the size of the adiabatic region is well- reproduced. Trapping probability is well- described. Massimo GiovannozziOxford - July 4th Hénon-like model Size of non-adiabatic region Pendulum-like model

Massimo GiovannozziOxford - July 4th Analytical computation of islands parameters Using perturbative theory (normal forms) it is possible to derive analytical estimate of islands parameters. Distance of fixed points from origin of phase space Distance between separatices Normalised phase space Islands surface Distance from resonance Secondary frequency

Massimo GiovannozziOxford - July 4th Operational implementation - I Sextupoles and octupoles are used to Generate stable islands Control size/position of islands Control linear chromaticity Control non-linear coupling (using an additional set of octupoles, normally used to combat instabilities) h 2,0 -> detuning with amplitude (H-plane) -> x 2 K 3 h 1,1 -> non-linear coupling -> x y K 3 h 0,2 -> detuning with amplitude (V-plane) -> y 2 K 3

Massimo GiovannozziOxford - July 4th Operational implementation - II Injection: s Extraction: s

Transverse dynamics - III Massimo GiovannozziOxford - July 4th Phase space at septum

Massimo GiovannozziOxford - July 4th Evolution of beam distribution Horizontal beam profiles in section 54 have been taken during the capture process (total intensity ~ 2.1×10 13 ).

Trapping performance 26Oxford - July 4th 2013Massimo Giovannozzi 20% trapping 18% trapping 5 PS turns

Extraction efficiency 27Oxford - July 4th 2013Massimo Giovannozzi Regular fluctuations in the extraction efficiency are also observed and seem well correlated to spill fluctuations. Distribution of extraction efficiency is peaked at about 98% (NB: the beam is debunched at extraction! Unavoidable beam losses are estimated at about 1-2%) CT extraction efficiency is about 93%

CT vs. MTE: extraction losses For the same extracted intensity, the CT features more losses, about the double, compared to MTE. The CT losses are spread around the ring whereas for MTE the losses are more concentrated on the extraction septum as anticipated in the MTE Design Report. CTMTE 28Oxford - July 4th 2013Massimo Giovannozzi

First observations of intensity- dependent effects - I Usual process for trapping the beam into stable islands. Varying parameter: total beam intensity. Massimo GiovannozziOxford - July 4th Beamlets are moving with intensity!

First observations of intensity- dependent effects - II The observed effect can be explained with an intensity- dependent shift of the single particle tune. Possible sources: Image currents. Direct effects (interaction between beamlets). Massimo GiovannozziOxford - July 4th Consider projection effect No change in beamlets size

Massimo GiovannozziOxford - July 4th Summary and Outlook - I A novel multi-turn extraction is studied since a few years: it allows manipulating transverse emittances in a synchrotron! First MTE beam delivered to the SPS by mid-September 2009 (about 1.5×10 13 p/extraction). Equal sharing for islands/core achieved by the end of In February 2010 the commissioning was resumed. High intensity beam was extracted (about 2.1×10 13 p/extraction) with record intensity 2.6×10 13 p/extraction physics run at SPS was started using MTE beam. Open issues: Variation of the fraction of particles trapped in islands. Activation of extraction septum due to the longitudinal structure of the beam (de-bunched as needed by the SPS). New optimised extraction scheme to avoid losses on extraction septum -> beam commissioning in 2014.

Massimo GiovannozziOxford - July 4th Summary and Outlook - II The same principle can be used for injection. Transverse shaping is possible, i.e. generation of hollow bunches. Lines of research: Complete study of splitting process in 2D and extend to 4D. Study trapping in 4D, i.e., manipulations in x-y plane. Study intensity-dependent effects. And many more!

Massimo GiovannozziOxford - July 4th Selected references S. Gilardoni, M. Giovannozzi, C. Hernalsteens (2013). First observations of intensity-dependent effects for transversely split beams during multiturn extraction studies at the CERN Proton Synchrotron, Phys. Rev. ST Accel. Beams. M. Giovannozzi, D. Quatraro, G. Turchetti, (2009). Generating unstable resonances for extraction schemes based on transverse splitting, Phys. Rev. ST Accel. Beams A. Franchi, S. Gilardoni, M. Giovannozzi, (2009). Progresses in the studies of adiabatic splitting of charged particle beams by crossing nonlinear resonances, Phys. Rev. ST Accel. Beams M. Giovannozzi and J. Morel, (2007). Principle and analysis of multiturn injection using stable islands of transverse phase space, Phys. Rev. ST Accel. Beams S. Gilardoni, M. Giovannozzi, M. Martini, E. Métral, P. Scaramuzzi, R. Steerenberg, A.-S. Müller, (2006). Experimental evidence of adiabatic splitting of charged particle beams using stable islands of transverse phase space, Phys. Rev. ST Accel. Beams R. Cappi, M. Giovannozzi, (2003). Multi-turn Extraction and Injection by Means of Adiabatic Capture in Stable Islands of Phase Space, Phys. Rev. ST Accel. Beams R. Cappi, M. Giovannozzi, (2002). Novel Method for Multi-Turn Extraction: Trapping Charged Particles in Islands of Phase Space, Phys. Rev. Lett The same principle can be used for injection.